Trigger a new Storyline project to open

Depends on how you are distributing it, most LMSs these days will manage languages. If not possible you could try and combine which is the easiest. Or embed them all as web objects with a trigger to mark complete via javascript. Or you could try something like simple scorm packager.

Your method will not work as it will need all the files not just the web page

Question: Are you making duplicates of all the slides and the only thing that is changing on the slide is the text? If so, you could start at the beginning and asking the learner to choose the language. Then setup so SL only shows that particular language.

My main concern was the branching/triggers but I just ran a test and actually it imported just fine using the import>Storyline. Thanks Phil!